Experimental Investigation on the Shear Strength Parameters and Deformability Behavior of Various Soil Types Mixed with Tire-Derived Aggregate

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Stockpiles of waste tires have become a serious environmental problem in Canada and worldwide. According to the Rubber Association of Canada, approximately 28 million scrap tires are generated annually in Canada, including 940,000 in Nova Scotia (Pehlken and Essadiqi 2005). The use of tire-derived aggregate (TDA) in civil engineering applications has been studied for many years. Using TDA alone has a self-ignition and high compressibility problem. Mixing TDA content with soil has great potential as a light filling material. Several studies have been carried out in the past to investigate the effect of TDA content mainly smaller than 20 mm in length on the shear strength behavior of a single type of soil especially sandy soil. However, limited studies have been conducted on TDA alone larger than 20 mm in length or the TDA content mixed with various soil types. Hence, to cover the limitations of previous studies, a series of large-scale direct shear box (305 mm × 305 mm × 220 mm) tests were performed on TDA alone with sizes up to 75 mm in length, and mixed with various soil types. Three types of soil including gravelly soil (coarse grain), sandy soil (medium grain), and clayey soil (fine grain) were selected to mix with the TDA content. First, the physical properties of the soils and TDA were determined. Next, TDA content was added to each soil type from 0 to 100% by weight, and each mixture was compacted using standard proctor energy. Then, the direct shear tests were conducted on the mixtures at the confining pressures of 50.1, 98.8 and 196.4 kPa. Test results showed that the addition of TDA content to the soils considerably decreases the dry unit weight of the mixtures. Also, adding TDA content to the gravel reduces the shear resistance of the mixtures upon shearing at all the confining pressures. However, the addition of TDA content up to 10% by weight to the clay and sand increases the shear resistance of the mixtures upon shearing significantly. It was found that except for the clay alone, adding more than 25% TDA content to the soils increases the compressibility behavior of the mixtures significantly. Test results also indicate that the addition of up to 25% TDA content by weight to the gravel and sand does not change the angle of internal friction considerably. However, adding up to 10% TDA content by weight to the clay increases the internal friction angle, from 18.8 to 32.3º. The addition of TDA content to the soils also contributes to a strain-hardening behavior in the mixtures. Also, adding TDA content to the mixtures decreases the normalized lateral earth pressure at-rest.